This invention is directed towards liquid chromatography utilizing gradient elution which actually is the changing of the chemical composition of the mobile phase or the eluent as a function of time which improves the performance of the chromatography system especially when one has samples that contain components which vary widely in chemical properties. The usual arrangement for this type of device is shown, for example, in the prior art as in U.S. Pat. No. 4,032,445 and in the literature, for example, in L. R. Snyder and J. J. Kirkland, "Introduction To Modern Liquid Chromatography," Wiley & Sons, N.Y. 1978, page 115.
A problem arises as the use of gradient elution for the changing eluent composition can produce a signal of its own, and when this occurs, the detector will yield a base line which may rise inasmuch as the gradient produces a detector response of its own. When a base line becomes non linear a detection in quantitative analysis is difficult or next to impossible in many situations.
Some attempts in the past have been made to correct the problem by splitting the high pressure flow line leading into the column and diverting part of the flow through the reference cell. It is difficult, however, to equalize the flow that is diverted into a reference cell to that in the main high pressure sample cell. One of the reasons behind this is that it is almost impossible to produce two columns which give exactly equal pressure drops, and this is an absolute necessity since variation in pressure will produce flow rate variations and in turn variations in retention times. Secondly, even if such an approach were feasible, column expense would be a major deterrent as columns are rather costly and have a limited lifetime.